implemented decfsz Instruction

Co-authored-by: Darkress <30271678+DarkressX@users.noreply.github.com>
Reviewed-on: darkress/pic16f84-sim#11

de/darkress/pic16f84sim/Main.java

@@ -15,8 +15,11 @@ class Main
         int input1 = 0x27FF;
         program.add(CommandDecoder.decode(0x3011)); //Write 0x11 to W
         Memory.setRegister(0x14, 0x01);
-        program.add(CommandDecoder.decode(0x0314));
-        for(int i = 0; i < 2; i++)
+        program.add(CommandDecoder.decode(0x0B94));
+        program.add(CommandDecoder.decode(0x0B94));
+        program.add(CommandDecoder.decode(0x0B94));
+        program.add(CommandDecoder.decode(0x3F05));
+        for(int i = 0; i < program.size(); i++)
         {
             program.get(ProgramCounter.getPc()).execute();
         }

de/darkress/pic16f84sim/commands/Decfsz.java

@@ -0,0 +1,33 @@
+package de.darkress.pic16f84sim.commands;
+
+import de.darkress.pic16f84sim.microcontroller.Memory;
+import de.darkress.pic16f84sim.microcontroller.ProgramCounter;
+
+public class Decfsz extends FileRegisterCommandUtils implements Command
+{
+    private final int address;
+    private final boolean destinationBit;
+
+    public Decfsz(int input)
+    {
+        address = input & 0x007F;
+        destinationBit = checkDestinationBit(input);
+    }
+
+    @Override
+    public void execute()
+    {
+        int result = Memory.getRegister(address) + 255; // Allow underflow
+
+        checkZeroBit(result);
+
+        writeToDestination(destinationBit, address, result % 256); // Catch underflow
+
+        if((result % 256) == 0)
+        {
+            Nop nop = new Nop();
+            nop.execute();
+        }
+        ProgramCounter.incPC();
+    }
+}

de/darkress/pic16f84sim/decoder/CommandDecoder.java

@@ -17,8 +17,7 @@ public class CommandDecoder
             case 0x300:
                 return new Decf(input);
             case 0xB00:
-                //decfsz();
-                break;
+                return new Decfsz(input);
             case 0xA00:
                 //incf();
                 break;